1. Field of the Invention
The present invention relates to a semiconductor device including a semiconductor element and a manufacturing method thereof
2. Description of the Related Art
Various metal oxides are used for a variety of applications.
Indium oxide is a well-known material and is used as a transparent electrode material which is necessary for liquid crystal displays and the like.
Some metal oxides have semiconductor characteristics. For example, tungsten oxide, tin oxide, indium oxide, zinc oxide, and the like can be given as metal oxides exhibiting semiconductor characteristics. References disclose a thin film transistor in which such a metal oxide exhibiting semiconductor characteristics is used for a channel formation region (Patent Documents 1 to 4, and Non-Patent Document 1).
Examples of metal oxides include not only an oxide of a single metal element but also an oxide of a plurality of metal elements (multi-component). For example, InGaO3(ZnO)m (m is a natural number) having homologous series has been known as a multi-component oxide semiconductor including In, Ga, and Zn (Non-Patent Documents 2 to 4).
Furthermore, it is proved that an oxide semiconductor including an In—Ga—Zn-based oxide is applicable to a channel layer of a thin film transistor (Patent Document 5 and Non-Patent Documents 5 and 6).
In a conventional technique, amorphous silicon or polycrystalline silicon has been used for a thin film transistor (a TFT) provided for each pixel of an active matrix liquid crystal display. However, in place of these silicon materials, attention has been attracted to a technique for manufacturing a thin film transistor including the metal oxide semiconductor described above. For example, Patent Documents 6 to 9 disclose a technique in which a thin film transistor is formed using zinc oxide or an In—Ga—Zn—O-based oxide semiconductor as a metal oxide semiconductor and is used as a switching element or the like of an image display device. It is also known that semiconductors including elements of Group 14 other than silicon and compound semiconductors other than the oxide semiconductor described above can be used for a channel layer of a transistor.
An oxide semiconductor film can be deposited at temperature of 300° C. or lower by a sputtering method or the like, and thin film transistors in each of which a channel formation region is formed using an oxide semiconductor can be easily formed in a wide region of a large substrate. Thus, application of oxide semiconductors to active matrix display devices has been expected.